Grid structures of ion beam etching (ibe) systems

ABSTRACT

The present disclosure relates to an ion beam etching (IBE) system including a plasma chamber configured to provide plasma, a screen grid, an extraction grid, an accelerator grid, and a decelerator grid. The screen grid receives a screen grid voltage to extract ions from the plasma within the plasma chamber to form an ion beam through a hole. The extraction grid receives an extraction grid voltage, where a voltage difference between the screen grid voltage and the extraction grid voltage determines an ion current density of the ion beam. The accelerator grid receives an accelerator grid voltage. A voltage difference between the extraction grid voltage and the accelerator grid voltage determines an ion beam energy for the ion beam. The IBE system can further includes a deflector system having a first deflector plate and a second deflector plate around a hole to control the direction of the ion beam.

BACKGROUND

With advances in semiconductor technology, there has been an increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices. Such scaling down has increased the complexity of semiconductormanufacturing processes and the demands for the precision of features insemiconductor manufacturing systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures.

FIGS. 1A-1B and 1D illustrate cross-sectional views of portions of anion beam etching (IBE) system with four grids, in accordance with someembodiments.

FIG. 1C illustrates voltages across different grids of an ion beametching (IBE) system, in accordance with some embodiments.

FIGS. 1E-1J illustrate cross-sectional views of portions of an IBEsystem with five grids, in accordance with some embodiments.

FIGS. 2A-2C illustrate isometric view and cross-sectional views of asemiconductor device with contact structures formed using an IBE system,in accordance with some embodiments.

FIGS. 2D-2G illustrate cross-sectional views of a semiconductor devicewith contact structures at various stages of its fabrication processusing an IBE system, in accordance with some embodiments.

FIGS. 2H-2J illustrate top views of a semiconductor device with contactstructures formed using an IBE system, in accordance with someembodiments.

FIG. 3 is a flow chart of a method for performing directional etchingusing an IBE system with four or five grids, in accordance with someembodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Asused herein, the formation of a first feature on a second feature meansthe first feature is formed in direct contact with the second feature.In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition does not in itselfdictate a relationship between the various embodiments and/orconfigurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “exemplary,” etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

In some embodiments, the terms “about” and “substantially” can indicatea value of a given quantity that varies within 5% of the value (e.g.,±1%, ±2%, ±3%, ±4%, ±5% of the value). These values are merely examplesand are not intended to be limiting. The terms “about” and“substantially” can refer to a percentage of the values as interpretedby those skilled in relevant art(s) in light of the teachings herein.

Ion beam etching (IBE) is a process that utilizes an inert gas plasma tobombard an etching target (e.g., a wafer) with ions to remove materialsfrom the wafer. An IBE system includes a plasma chamber and a multi-gridsystem which is an optics system. Current IBE systems include athree-grid system having three grids. The three-grid system has numerouselectrostatic apertures (holes) separated from each other, e.g.,sometimes by a few millimeters. Applying specific voltages to each grid,the three-grid system controls the holes and ion beams through theholes. In detail, the three-grid system extracts positively charged ionsfrom inductively coupled plasma (ICP, also referred to as inductivelycoupled discharge plasma) generated in the plasma chamber. In addition,the three-grid system further accelerates and directs the ions throughthe holes to form mono-energetic beams of the ions, or ion beams, toetch materials by physical sputtering on the wafer. Controlled by thethree-grid system, an individual ion beam is created through each hole.The combination of the ion beams controlled by the three-grid systemform a single broad beam to bombard the etching target. In an IBEprocess, an etching target (e.g., a wafer) can be placed with a tiltedangle and/or a rotated angle to allow an angle of incidence of the ionsonto the surface of the wafer. Such control of the ion incidence on thewafer affects sputtering yield and the resulting topography, hencesubstantially improving etching profiles of the etching target.

Accordingly, an IBE process can provide directional flexibility that isnot available in other plasma processes. An IBE system can perform adirectional etching process to create a feature (e.g., an opening) on aphotoresist layer or a physical layer of a wafer, where the opening canhave different lengths in different dimensions. For example, an IBEsystem can expand a square opening with a critical dimension (CD) to belarger in one dimension along an X-axis without changing a dimensionalong a Y-axis. As a result, the IBE process can compensate the extremeultraviolet (EUV) lithography resolution limitation at small criticaldimension patterning. While the etching rate with the IBE process istypically lower than the etching rate for a reactive ion etching (RIE)process, the IBE process can offer a high precision for applicationsthat demand high dimension profile control. Also, the IBE process can beused to remove materials where an RIE process may not be successful. TheIBE process can etch alloys and composite materials that are notcompatible with an RIE process.

One of the challenges of the IBE process can be preventing asymmetryetching. When a wafer is placed within a process chamber of an IBEsystem with a tilted angle and/or rotated angle, different ion beamsthrough the holes of the three-grid system have different incidencedistances to the wafer. An incidence distance of an ion beam to thewafer is a distance from the source of the ion, or simply referred to asan ion source, to a location of the wafer, where the location is anincidence point of the ion beam on the surface of the wafer. Therefore,ions in different ion beams travel different incidence distances toreach the different locations of the wafer surface, resulting indifferent etching rates at different locations of the wafer surface. Theetching rate at a first location of the tilted wafer by a first ion beamis lower when an incidence distance of the first ion beam is longer,while the etching rate at a second location of the tilted wafer by asecond ion beam is higher when an incidence distance of the second ionbeam is shorter. As a result, the etching amount at the first locationis smaller than the etching amount at the second location, resulting inan asymmetry etching behavior for the IBE process. In general, theetching rate at a location of a tilted wafer surface is inverselyproportional to an incidence distance of the corresponding ion beamincidence to the location. Rotation of the tilted wafer does notovercome the challenges of preventing asymmetry etching.

In an IBE system, the three-grid system includes a screen grid, anaccelerator grid, and a decelerator grid to control the ion beams tostrike the wafer. The screen grid, the accelerator grid, or thedecelerator grid, includes elements, such as screen grid elements,accelerator grid elements, and decelerator grid elements. A screen gridelement, an accelerator grid element, and a decelerator grid elementtogether control a hole and an ion beam through the hole. All the screengrid elements are supplied by a screen voltage, all the accelerator gridelements are supplied by an accelerator voltage, and all the deceleratorgrid elements are supplied by a decelerator voltage. Therefore, all theion beams of the IBE systems are controlled by electric fields of thesame energy. Under the same energy, when ions in two different ion beamsgo through two different incidence distances to reach two locations ofthe wafer surface, two different etching rates are resulted at the twolocations.

The present disclosure provides example IBE systems that can generatesubstantially uniformly etching across different locations of a surfaceof a tilted wafer within the process chamber of the IBE systems. In someembodiments, an IBE system can include at least a four-grid system witha screen grid having screen grid elements, an extraction grid havingextraction grid elements, an accelerator grid having accelerator gridelements, and a decelerator grid having decelerator grid elements. Ascreen grid element, an extraction grid element, an accelerator gridelement, and a decelerator grid element can form a hole that extendsthrough the screen grid, the extraction grid, the accelerator grid, andthe decelerator grid. The screen grid receives a screen grid voltage toextract ions from the plasma within the plasma chamber to form an ionbeam through the hole. The extraction grid receives an extraction gridvoltage, where a voltage difference between the screen grid voltage andthe extraction grid voltage determines an ion current density of the ionbeam through the hole. The accelerator grid receives an accelerator gridvoltage, where a voltage difference between the extraction grid voltageand the accelerator grid voltage determines an ion beam energy of theion beam through the hole. The decelerator grid receives a deceleratorgrid voltage. The addition of the extraction grid can provide additionalcontrol to the ion beam energy for the ion beam through the hole,reducing the asymmetry etching of the etching target, e.g., a wafer.

In some embodiments, in addition to a four-grid system, an IBE systemcan include a deflector system having deflector plates, where thedeflector system can be counted as a fifth grid. A first deflector plateand a second deflector plate can be separated by a gap and disposedaround a hole through the screen grid, the extraction grid, theaccelerator grid, and the decelerator grid. The first deflector platecan receive a first deflector voltage, and the second deflector platecan receive a second deflector voltage, where a voltage differencebetween the first deflector voltage and the second deflector voltage candetermine a trajectory of the ion beam through the hole and the gapbetween the first deflector plate and the second deflector plate. Thetrajectory of the ion beam can include a tilt angle of the ion beam toreach a wafer surface to perform directional etching of the wafer. Theaddition of the deflector system can provide additional control andprecision to the ion beam direction through the hole to reach the wafer,reducing the asymmetry etching of the etching target, e.g., a wafer.

In some embodiments, the voltages supplied to the accelerator gridelements or the deflector plates around different holes can be varied tocontrol different ion beams. Instead of having a same voltage suppliedto different accelerator grid elements, some embodiments have differentvoltages supplied to different accelerator grid elements. Accordingly,the voltages for accelerator grid elements and deflector plates canbalance all locations in the rotated tilted wafer with equal directionaletching. As a result, embodiments herein reduce IBE asymmetry etchingbehavior. A tilted wafer has uniform etching across different locationsof a surface of the tilted wafer when an etching amount at a firstlocation is substantially same as an etching amount at a secondlocation, where the first location and the second location can be anylocation of the surface of the tilted wafer.

FIGS. 1A-1B and 1D illustrate cross-sectional views of portions of anIBE system 100 with four grids including a screen grid 110, anextraction grid 115, an accelerator grid 120, and a decelerator grid130, in accordance with some embodiments. FIG. 1C illustrates voltagesacross screen grid 110, extraction grid 115, accelerator grid 120, anddecelerator grid 130. FIGS. 1E-1J illustrate cross-sectional views ofportions of IBE system 100 with five grids including screen grid 110,extraction grid 115, accelerator grid 120, decelerator grid 130, adeflector system 134, or a deflector system 137, in accordance with someembodiments.

In some embodiments, as shown in FIG. 1A, IBE system 100 can include aprocess chamber 101 having an inlet 102 to receive an inert gas, such asa noble gas. Process chamber 101 can include a plasma chamber 103configured to provide plasma, and a grid system 150 including screengrid 110, extraction grid 115, accelerator grid 120, and deceleratorgrid 130. Holes are disposed in grid system 150, such as a hole 151, ahole 152, and a hole 153, with more details shown in FIG. 1B. Ionsgenerated from the plasma within plasma chamber 103 go through the holesto form ion beams, such as an ion beam 141, an ion beam 142, and an ionbeam 143. In addition, process chamber 101 can include a control unit104, a mechanical shutter 105, a plasma bridge neutralizer 106, arotating fixture 107 configured to hold a wafer 154, a secondary ionsmass spectrometer 108, and a pump 109 to pre-pump and exhaust processchamber 101. Wafer 154 can have a tilted angle θ with respect to a firstdirection (e.g., along a Y-axis) and a rotated angle α with respect to asecond direction (e.g., along a Z-axis). Rotating fixture 107 can rotatewafer 154. In some embodiments, ion beam 141, ion beam 142, and ion beam143 can reach wafer 154 along a third direction (e.g., along an X-axis).

IBE system 100 can use an inert gas (e.g., argon or a noble gas)received from inlet 102 to generate ICP in plasma chamber 103. Inaddition, being electrically biased, grid system 150 can extractpositively charged ions from the ICP and provide ions as ion beamsthrough the holes of grid system 150 to bombard wafer 154 to removematerial from wafer 154. For example, argon ions can be extracted froman ICP source, accelerated and directed by grid system 150 to formmono-energetic beams, such as ion beam 141, ion beam 142, and ion beam143 to etch any materials, such as piezoelectric and ferroelectrics,magnetics materials, group III-V elements of the periodic table (e.g.,GaAs, InP, GaN, AlN . . . ), ohmic metals (e.g., Au, Pt, Cu, Ir . . . ),and hard mask materials (e.g., Ag, TiWN, Ni, . . . ) on wafer 154. Insome embodiments, IBE system 100 can have a wide range energy capability(from about 50 V to about 800 V) for low ion damage or for fast etch ofvarious materials.

In some embodiments, plasma chamber 103, which can be an ICP source, caninclude a 350 mm diameter quartz vessel with a radio frequency (RF)plasma generator. An antenna (not shown) can be wrapped around thequartz vessel for inductive coupling. The antenna can operate at about1.8 MHz and about 2 kW power. The oscillating current in the antenna atabout 1.8 MHz can induce an electromagnetic field in the quartz vessel.During plasma ignition, some primary electrons can collect theelectromagnetic field energy and agitate accordingly. Main plasma can becreated inside the quartz vessel of plasma chamber 103 by inelasticcollisions between hot electrons and neutrals (injected Argon gas) whichgenerate ions/electrons pairs.

Grid system 150 can extract ions from plasma within plasma chamber 103,and accelerate the ions to build mono-energetic beams, such as ion beam141, ion beam 142, and ion beam 143 through the holes of grid system150. This can be done by applying specific voltages to each grid of gridsystem 150, which will be shown in more details in FIG. 1B. The innergrid, which is screen grid 110, can be in contact with plasma chamber103, and can receive a screen grid voltage to extract ions from theplasma within plasma chamber 103 to form an ion beam, such as ion beam141, ion beam 142, and ion beam 143, through the holes of grid system150. Positive ions in the plasma within plasma chamber 103 that driftclose to screen grid 110 can be extracted through the holes, whileelectrons can be separated and kept inside plasma source 103. There aresome space shown in FIG. 1A between screen grid 110 and plasma chamber103 for illustration purposes. The second grid, which is extraction grid115, can receive an extraction grid voltage. A voltage differencebetween the screen grid voltage and the extraction grid voltage candetermine an ion current density of the ion beam, such as ion beam 141,ion beam 142, and ion beam 143, through the holes of grid system 150.The third grid, which is accelerator grid 120, can receive anaccelerator grid voltage. A voltage difference between the extractiongrid voltage and the accelerator grid voltage can determine an ion beamenergy for the ion beam, such as ion beam 141, ion beam 142, and ionbeam 143, through the holes of grid system 150. The fourth grid, whichis decelerator grid 130, can be held at ground voltage. Decelerator grid130 reduces divergence of the ion beams and can create another electricfield which can prevent electrons emitted by plasma bridge neutralizer106 from back-streaming into grid system 150.

Mechanical shutter 105 can be placed downstream of grid system 150. Whenclosed, process chamber 101 is protected and no etching takes place.This closed position allows for stabilization of the different partssuch as plasma source, beam voltage, ions acceleration, and more.Mechanical shutter 105 is open when the whole system is stable (e.g.ions beam fully collimated and mon-energetic, substrate fixturecorrectly clamped and cooled-down, etc.) to ensure constant, precise,and repeatable processes.

Plasma bridge neutralizer (PBN) 106 is an electrons source placeddownstream from grid system 150 to neutralize the charged ion beam. Theelectrons cannot back-stream into grid system 150 because of thenegative decelerator-accelerator electric field. These electrons do notcombine with the ions present in the beam, but they provide a chargebalance for the ions in order to avoid space or surface charging onwafer 154.

Secondary ions mass spectrometer 108 can be used to monitor sputteredmaterial species, allowing etching to be stopped at specific layers.When wafer 154 is bombarded by the ion beams, such as ion beam 141, ionbeam 142, and ion beam 143, secondary ions can be ejected from thesurface of wafer 154. These ejected secondary ions can be collected anda mass analyzer (quadrupole) can isolate them according to their mass inorder to determine the elemental composition of the sputtered surface. Adetection system (electron multiplier) can amplify and display thecounts (magnitude) of the secondary ions in real time.

In addition, IBE system 100 can include other structural and functionalcomponents, such as RF generators, matching circuits, chamber liners,control circuits, actuators, power supplies, exhaust systems, etc. whichare not shown for simplicity.

FIG. 1B illustrates further details of grid system 150 including screengrid 110, extraction grid 115, accelerator grid 120, and deceleratorgrid 130. Screen grid 110 can include screen grid elements, such as ascreen grid element 111, a screen grid element 112, and a screen gridelement 113. The screen grid elements, such as screen grid element 111,screen grid element 112, and screen grid element 113, are in contactwith plasma chamber 103. Extraction grid 115 is disposed adjacent to andseparated from screen grid 110. Extraction grid 115 includes extractiongrid elements, such as an extraction grid element 116, an extractiongrid element 117, and an extraction grid element 118. Accelerator grid120 is disposed adjacent to and separated from extraction grid 115.Accelerator grid 120 includes accelerator grid elements, such as anaccelerator grid element 121, an accelerator grid element 122, and anaccelerator grid element 123. Decelerator grid 130 is disposed adjacentto and separated from accelerator grid 120. Decelerator grid 130includes decelerator grid elements, such as a decelerator grid element131, a decelerator grid element 132, and a decelerator grid element 133.Grid system 150 includes holes, such as hole 151, hole 152, and hole153. Holes 151, 152, and 153 extend through screen grid 110, extractiongrid 115, accelerator grid 120, and decelerator grid 130. In someembodiments, the holes, such as hole 151, hole 152, and hole 153,include molybdenum electrostatic apertures of various diameters atdifferent grid elements. For example, hole 151 includes an aperture 161at screen grid 110, an aperture 162 at extraction grid 115, an aperture163 at accelerator grid 120, and an aperture 164 at decelerator grid130. Apertures 161, 162, 163, and 164 have different diameters. Moredetails of hole 151 are shown in FIGS. 1H and 1J.

In some embodiments, a screen grid voltage 124 is supplied to screengrid 110 to extract ions from the plasma within plasma chamber 103 toform ion beam 141 through hole 151. An extraction grid voltage 125 issupplied to extraction grid 115, where a voltage difference betweenscreen grid voltage 124 and extraction grid voltage 125 can determine anion current density of ion beam 141 through hole 151. An acceleratorgrid voltage 126 is supplied to accelerator grid 120, where a voltagedifference between extraction grid voltage 125 and accelerator gridvoltage 126 can determine an ion beam energy for ion beam 141 throughhole 151. A decelerator grid voltage 127 is supplied to decelerator grid130. In some embodiments, decelerator grid voltage 127 can be a groundvoltage.

In some embodiments, control unit 104 is configured to control variousoperations of IBE system 100, e.g., supplying voltages for grid system150. In some embodiments, as shown in FIG. 1C, screen grid voltage 124is a positive voltage with respect to a ground voltage, extraction gridvoltage 125 is also a positive voltage with respect to the groundvoltage, accelerator grid voltage 126 is a negative voltage with respectto the ground voltage, and decelerator grid voltage 127 is the groundvoltage. In some embodiments, screen grid voltage 124 can be about 1000volt to about 1200 volt, extraction grid voltage 125 can be about 800volt to about 1000 volt, accelerator grid voltage 126 can be about −200volt to about −400 volt, and decelerator grid voltage 127 can be theground voltage. In some embodiments, different voltages can be suppliedto different accelerator grid elements.

Ions generated from the plasma within plasma chamber 103 go through theholes to form ion beams, such as ion beam 141 through hole 151, ion beam142 through hole 152, and ion beam 143 through hole 153. The ion beamsperform directional etching on wafer 154. An ion beam through a hole iscontrolled by a combination of a screen grid element, an extraction gridelement, an accelerator grid element, and a decelerator grid element.

In some embodiments, as shown in FIG. 1D, ion beam 141 is controlled byscreen grid element 111, extraction grid element 116, accelerator gridelement 121, and decelerator grid element 131. Ion beam 141 reaches thesurface of wafer 154 at an incidence point 155. Hence, ion beam 141 hasan incidence distance E1 measured from the source of ion beam 141, or anion source, to point 155. The source of ion beam 141 can be counted asthe external edge of plasma chamber 103 where the ions are extractedfrom.

Referring back to FIG. 1B, similarly, ion beam 142 is controlled byscreen grid element 112, extraction grid element 117, accelerator gridelement 122, and decelerator grid element 132. Ion beam 143 iscontrolled by screen grid element 113, extraction grid element 118,accelerator grid element 123, and decelerator grid element 133. Ion beam142 has an incidence distance E2 measured from the source of ion beam142 to an incidence point 156 of ion beam 142. Ion beam 143 has anincidence distance E3 measured from the source of ion beam 143 to anincidence point 157 of ion beam 143. The source of ion beam 141, thesource of ion beam 142, and the source of ion beam 143, can be a same orparallel aligned. In some embodiments, the incidence distance E1, theincidence distance E2, and incidence distance E3, are different fromeach other.

Therefore, ions in different ion beams travel different incidencedistances to reach the different locations of the wafer surface. Thedifferences in the incidence distances of ion beams can result indifferent etching rates at different locations of the wafer surface,which may be referred to as asymmetry etching issue or pitch walkingissue. An etching rate at a point of wafer 154 can be a function of theenergy of the ions reaching the point and the distance of the ionstravel to reach the point, e.g., the incidence distance of the ion beam.In general, the etching rate at a location of a tilted wafer surface isnear inversely proportional to an incidence distance of thecorresponding ion beam incidence to the location. When all ion beams aresupplied by the same energy, the etching rate of incidence point 157 byion beam 143 can be lower than the etching rate of incidence point 156by ion beam 142, since the incidence distance of ion beam 143 is longerthan the incidence distance of ion beam 142. Rotation of the tiltedwafer would not be able to solve the asymmetry etching behavior problemfor the IBE process.

With the addition of extraction grid 115, the ion density and ion energyare decoupled in the four grids, where the ion current density arecontrolled by the screen grid and extraction grid. Ions energy areaccelerated via the electrostatic field between the extraction grid andthe accelerator grid. Embodiments here can adjust the voltage differencebetween screen grid voltage 124 and extraction grid voltage 125 toadjust the ion current density of ion beams through the holes, andfurther adjust the voltage difference between extraction grid voltage125 and accelerator grid voltage 126 to adjust an ion beam energy forion beams through the holes. By adjusting the various voltagedifferences, ion beams are supplied by different energy so that theetching rate can be the same at different locations.

FIGS. 1E-1J illustrate cross-sectional views of portions of IBE system100 with five grids including screen grid 110, extraction grid 115,accelerator grid 120, decelerator grid 130, deflector system 134, ordeflector system 137, in accordance with some embodiments. The additionof deflector system 134 or deflector system 137, which can be counted asa fifth grid, can provide additional control over the etching rate of awafer in different locations.

FIG. 1E illustrates further details of grid system 150 including screengrid 110, extraction grid 115, accelerator grid 120, decelerator grid130, and deflector system 134 including deflector plates, such as adeflector plate 135 and a deflector plate 136. Screen grid 110 caninclude screen grid elements, such as screen grid element 111, screengrid element 112, and screen grid element 113. Extraction grid 115includes extraction grid elements, such as extraction grid element 116,extraction grid element 117, and extraction grid element 118.Accelerator grid 120 includes accelerator grid elements, such asaccelerator grid element 121, accelerator grid element 122, andaccelerator grid element 123. Decelerator grid 130 includes deceleratorgrid elements, such as decelerator grid element 131, decelerator gridelement 132, and decelerator grid element 133. Grid system 150 includesholes, such as hole 151, hole 152, and hole 153. Holes 151, 152, and 153extend through screen grid 110, extraction grid 115, accelerator grid120, and decelerator grid 130. Ion beam 141 can go through hole 151 toreach location 155 of wafer 154 as shown in FIG. 1B and FIG. 1F.Similarly, ion beams 142 and 143 can go through respective holes 152 and153 to reach other locations of wafer 154.

In addition, grid system 150 includes deflector system 134 havingdeflector plate 135 and deflector plate 136, which are separated by agap 165 around hole 151. Similar deflector plates are formed aroundholes, such as hole 152 and hole 153. Deflector plate 135 and deflectorplate 136 can have a length of about 20 mm to 90 mm. Gap 165 can have aheight of about 5 mm to about 12 mm. Deflector plate 135 and deflectorplate 136 can be disposed between extraction grid 115 and acceleratorgrid 120.

Deflector plate 135 can receive a first deflector voltage, and deflectorplate 136 can receive a second deflector voltage. The first deflectorvoltage can have a first voltage polarity different from the secondvoltage polarity of the second deflector voltage. For example, the firstdeflector voltage is a positive voltage, and the second voltage is anegative voltage. A voltage difference between the first deflectorvoltage and the second deflector voltage determines a trajectory of ionbeam 141. As shown in FIG. 1F, when the voltage difference between thefirst deflector voltage and the second deflector voltage is zero, thetrajectory of ion beam 141 can be in parallel with an X-axis to reachlocation 155 of wafer 154 as if there was no deflector plate 135 anddeflector plate 136. On the other hand, as shown in FIG. 1G, when thevoltage difference between the first deflector voltage and the seconddeflector voltage is larger than zero, the trajectory of ion beam 141can have a tilt angle θ2 to reach location 155 of wafer 154 to performdirectional etching of the wafer, where wafer 154 is not tilted. Thetilt angle θ2 of ion beam 141 can depend on the voltage differencebetween the first deflector voltage and the second deflector voltage.

In some embodiments, as shown in FIG. 1F, control unit 104 can controlthe first deflector voltage to deflector plate 135 and the seconddeflector voltage to deflector plate 136 to have a first voltagedifference, e.g., zero voltage difference, to generate a firstdirectional etching effect at location 155 of wafer 154 when rotatingfixture 107 holds wafer 154 in a first tilt angle θ. As shown in FIG.1G, control unit 104 can control the first deflector voltage todeflector plate 135 and the second deflector voltage to deflector plate136 to have a second voltage difference so that ion beam 141 can have atilt angle θ2 while rotating fixture 107 holds wafer 154 in a secondtilt angle, e.g., zero degree. As a result, ion beam 141 reacheslocation 155 to generate a second directional etching effect at location155. Control unit 104 can adjust the first voltage difference and thesecond voltage difference to have the first directional etching effectto wafer 154 as the same as the second directional etching effect towafer 154, such as the same etching opening length or width.

As shown in FIG. 1H, in some embodiments, hole 151 includes aperture 161at screen grid 110, aperture 162 at extraction grid 115, aperture 163 ataccelerator grid 120, and aperture 164 at decelerator grid 130. Adiameter D1 of apertures 161 on screen grid 110 can be greater than adiameter D2 of aperture 162 on extraction grid 115. Diameter D2 ofaperture 162 is further smaller than a diameter D3 of aperture 163 onaccelerator grid 120. And a diameter D4 of aperture 164 on deceleratorgrid 130 can be greater than diameter D3 of aperture 163 on acceleratorgrid 120. In some embodiments, diameter D1 can range from about 4 mm toabout 7 mm. Diameter D2 can range from about 2 mm to about 5 mm.Diameter D3 can range from about 2 mm to about 6 mm. Diameter D4 canrange from about 3 mm to about 7 mm. In some embodiments, a difference61 between diameters D1 and D2 can range from about 0.5 mm to about 4mm. In some embodiments, a different 62 between diameters D3 and D4 canrange from about 0.5 mm to about 2.5 mm. Screen grid 110 with diameterD1 greater than diameter D2 of extraction grid 115 and D3 of acceleratorgrid 120 can increase the number of ions in ion beam 141 through hole151. Extraction grid 115 with diameter D2 and accelerator grid 120 withdiameter D3 less than diameter D1 can accelerate and focus ions in ionbeam 141. In some embodiments, diameter D1 can be greater than, lessthan, or the same as diameter D4.

In some embodiments, screen grid 110 can have a thickness T1 along anX-axis ranging from about 0.3 mm to about 0.8 mm. In some embodiments,extraction grid 115 can have a thickness T2 along an X-axis ranging fromabout 0.4 mm to about 1.0 mm. In some embodiments, accelerator grid 120can have a thickness T3 along an X-axis ranging from about 0.4 mm toabout 1.2 mm. In some embodiments, decelerator grid 130 can have athickness T4 along an X-axis ranging from about 0.4 mm to about 1.2 mm.

In some embodiments, a separation space S1 along an X-axis betweenscreen grid 110 and extraction grid 115 can range from about 0.4 mm toabout 0.6 mm. A separation space S2 along an X-axis between extractiongrid 115 and accelerator grid 120 can range from about 25 mm to about 45mm. A separation space S3 along an X-axis between accelerator grid 120and decelerator grid 130 can range from about 0.5 mm to about 0.7 mm.

In some embodiments, deflector plate 135 and deflector plate 136 areseparated by gap 165 of height H1 along an Y-axis in a range of about 5mm to about 8 mm. Deflector plate 135 and deflector plate 136 can have alength of about 22 mm to 40 mm. A ratio between the length of deflectorplate 135 and height H1 can be in a range of about 3 to about 8.Deflector plate 135 and deflector plate 136 can be disposed betweenextraction grid 115 and accelerator grid 120. Deflector plate 135 anddeflector plate 136 can be separated from extraction grid 115 along anX-axis by a distance 63 in a range of about 0.5 mm to about 8 mm.Deflector plate 136 can have a distance 64 below the surface ofextraction element 116, where 64 is in a range of about 0.5 mm to about8 mm.

With the configurations of screen grid 110, extraction grid 115,accelerator grid 120, and decelerator grid 130 as shown in FIGS. 1E-1H,ions in plasma chamber 103 can be focused through these grids withoutdirect interception and form ion beam 141 through hole 151. Deflectorplate 135 and deflector plate 136 can be used to control the directionof ion beam 141.

In some embodiments, deflector plate 135 and deflector plate 136 can beadjustable in positions, and move in an up direction or a down directionso that distance 84 can be larger or smaller. Deflector plate 135 anddeflector plate 136 can also move in a left direction or a rightdirection so that distance 83 can be larger or smaller. Deflector plate135 can move up and deflector plate 136 can move down so that gap 165can be wider. In addition, deflector plate 135 can move down anddeflector plate 136 can move up so that gap 165 can be narrower.

FIG. 1I illustrates further details of another example grid system 150including screen grid 110, extraction grid 115, accelerator grid 120,decelerator grid 130, and deflector system 137 including deflectorplates, such as a deflector plate 138 and a deflector plate 139. Thediscussion of deflector system 134 applies to deflector system 137,unless mentioned otherwise. Deflector system 137 can be placed in alocation different from the location of deflector system 134 shown inFIG. 1E-1H. Compared to deflector system 134 placed between extractiongrid 115 and the accelerator grid 120, deflector system 137 disposedadjacent to and separated from the decelerator grid can create a widertile angle for ion beam 141.

Screen grid 110 can include screen grid elements, such as screen gridelement 111, screen grid element 112, and screen grid element 113.Extraction grid 115 includes extraction grid elements, such asextraction grid element 116, extraction grid element 117, and extractiongrid element 118. Accelerator grid 120 includes accelerator gridelements, such as accelerator grid element 121, accelerator grid element122, and accelerator grid element 123. Decelerator grid 130 includesdecelerator grid elements, such as decelerator grid element 131,decelerator grid element 132, and decelerator grid element 133. Gridsystem 150 includes holes, such as hole 151, hole 152, and hole 153.Holes 151, 152, and 153 extend through screen grid 110, extraction grid115, accelerator grid 120, and decelerator grid 130. Ion beam 141 can gothrough hole 151 to reach a surface of a wafer, e.g., wafer 154 as shownin FIG. 1B. Similarly, ion beams 142 and 143 can go through respectiveholes 152 and 153 to reach other locations of wafer 154.

In addition, grid system 150 includes deflector system 137 havingdeflector plate 138 and deflector plate 139, which are separated by agap 166 around hole 151. Similar deflector plates are formed aroundother holes, such as hole 152 and hole 153. Deflector plate 138 anddeflector plate 139 can have a length of about 20 mm to 90 mm. Gap 166can have a height H2 of about 5 mm to about 12 mm. A ratio between thelength of deflector plate 138 and height H2 can be in a range of about 2to about 16. Deflector plate 138 and deflector plate 139 can be disposedadjacent to and separated from decelerator grid 130, and separated fromaccelerator grid 120 by decelerator grid 130.

Deflector plate 138 can receive a first deflector voltage, and deflectorplate 139 can receive a second deflector voltage. The first deflectorvoltage can have a first voltage polarity different from a secondvoltage polarity of the second deflector voltage. A voltage differencebetween the first deflector voltage and the second deflector voltagedetermines a trajectory of ion beam 141. The trajectory of ion beam 141can include a tilt angle of ion beam 141 to reach a wafer surface toperform directional etching of the wafer. The tilt angle of ion beam 141can depend on the voltage difference between the first deflector voltageand the second deflector voltage. The tilt angle of ion beam 141 and itsrelationship with the voltage difference between the first deflectorvoltage and the second deflector voltage can be similar to therelationship shown in FIGS. 1F-1G.

As shown in FIG. 1J, in some embodiments, hole 151 includes aperture 161at screen grid 110, aperture 162 at extraction grid 115, aperture 163 ataccelerator grid 120, and aperture 164 at decelerator grid 130. Adiameter D1 of apertures 161 on screen grid 110 can be greater than adiameter D2 of aperture 162 on extraction grid t 15. Diameter D2 ofaperture 162 is smaller than a diameter D3 of aperture 163 onaccelerator grid 120. A diameter D4 of aperture 164 on decelerator grid130 can be greater than diameter D3 of aperture 163 on accelerator grid120. In some embodiments, diameter D1 can range from about 4 mm to about7 mm. Diameter D2 can range from about 2 mm to about 5 mm. Diameter D3can range from about 2 mm to about 6 mm. Diameter D4 can range fromabout 3 mm to about 7 mm. In some embodiments, a difference S1 betweendiameters D1 and D2 can range from about 0.5 mm to about 4 mm. In someembodiments, a different 62 between diameters D3 and D4 can range fromabout 0.5 mm to about 2.5 mm. Screen grid 110 with diameter D1 greaterthan diameter D2 of extraction grid 115 and D3 of accelerator grid 120can increase the number of ions in ion beam 141 through hole 151.Extraction grid 115 with diameter D2 and accelerator grid 120 withdiameter D3 less than diameter D1 can accelerate and focus ions in ionbeam 141. In some embodiments, diameter D1 can be greater than, lessthan, or the same as diameter D4.

In some embodiments, screen grid 110 can have a thickness T1 along anX-axis ranging from about 0.3 mm to about 0.8 mm. In some embodiments,extraction grid 115 can have a thickness T2 along an X-axis ranging fromabout 0.4 mm to about 1.0 mm. In some embodiments, accelerator grid 120can have a thickness T3 along an X-axis ranging from about 0.4 mm toabout 1.2 mm. In some embodiments, decelerator grid 130 can have athickness T4 along an X-axis ranging from about 0.4 mm to about 1.2 mm.

In some embodiments, a separation space S1 along an X-axis betweenscreen grid 110 and extraction grid 115 can range from about 0.4 mm toabout 0.6 mm. A separation space S2 along an X-axis between extractiongrid 115 and accelerator grid 120 can range from about 25 mm to about 45mm. A separation space S3 along an X-axis between accelerator grid 120and decelerator grid 130 can range from about 0.5 mm to about 0.7 mm.

In some embodiments, deflector plate 138 and deflector plate 139 can beseparated by gap 166 of height H2 along an Y-axis in a range of about 7mm to about 9 mm. Deflector plate 138 and deflector plate 139 can have alength of about 40 mm to about 80 mm. A ratio between the length ofdeflector plate 138 and height H2 can be in a range of about 2 to about16. Deflector plate 138 and deflector plate 139 can be disposed adjacentto and separated from decelerator grid 130. Deflector plate 138 anddeflector plate 139 can be separated from decelerator grid 130 along anX-axis by a distance 85 in a range of about 0.5 mm to about 8 mm.Deflector plate 139 can have a distance 86 below the surface ofdecelerator element 131, where 66 is in range of about 0.5 mm to about 8mm.

With the configurations of screen grid 110, extraction grid 115,accelerator grid 120, and decelerator grid 130 as shown in FIGS. 1I-1J,ions in plasma chamber 103 can be focused through these grids withoutdirect interception and form ion beam 141 through hole 151. Deflectorplate 138 and deflector plate 139 can be used to control the directionof ion beam 141.

In some embodiments, deflector plate 138 and deflector plate 139 can beadjustable in positions, and move in an up direction or a down directionso that distance 66 can be larger or smaller. Deflector plate 138 anddeflector plate 139 can also move in a left direction or a rightdirection so that distance 65 can be larger or smaller. Deflector plate138 can move up and deflector plate 139 can move down so that gap 166can be wider. In addition, deflector plate 138 can move down anddeflector plate 139 can move up so that gap 165 can be narrower.

FIG. 2A illustrates an isometric view of a field effect transistor (FET)200 (also referred to as semiconductor device 200) after the formationof gate contact structures 232 using IBE system 100, according to someembodiments. FIGS. 2B, 2D, and 2F illustrate cross-sectional views ofFET 200 along line A-A of FIG. 2A and FIGS. 2C, 2E, and 2G illustratecross-sectional views along line B-B of FIG. 2A with additionalstructures that are not shown in FIG. 2A for simplicity. The discussionof elements in FIGS. 2A-2G with the same annotations applies to eachother, unless mentioned otherwise. In some embodiments, FET 200 canrepresent n-type FET 200 (NFET 200) or p-type FET 200 (PFET 200) and thediscussion of FET 200 applies to both NFET 200 and PFET 200, unlessmentioned otherwise.

Referring to FIG. 2A, FET 200 can include an array of gate structures212 disposed on a fin structure 208, gate contact structures 232disposed on gate structures 212, an array of S/D regions 210 (one of S/Dregions 210 visible in FIG. 2A) disposed on portions of fin structure208 that are not covered by gate structures 212, and S/D contactstructures 230 (one of S/D contact structures 230 visible in FIG. 2A).FET 200 can further include gate spacers 216, shallow trench isolation(STI) regions 219, etch stop layers (ESLs) 217A-217B, and interlayerdielectric (ILD) layers 218A-218C. In some embodiments, gate spacers216, STI regions 219, ESLs 217A-217B, and ILD layers 218A-218C caninclude an insulating material, such as silicon oxide, silicon nitride(SiN), silicon carbon nitride (SiCN), silicon oxycarbon nitride (SiOCN),and silicon germanium oxide.

FET 200 can be formed on a substrate 206. There may be other FETs and/orstructures (e.g., isolation structures) formed on substrate 206.Substrate 206 can be a semiconductor material, such as silicon,germanium (Ge), silicon germanium (SiGe), a silicon-on-insulator (SOI)structure, and a combination thereof. In some embodiments, fin structure208 can include a material similar to substrate 206 and extend along anX-axis.

Referring to FIGS. 2A-2B, S/D regions 210 can include epitaxially-grownsemiconductor material, such as Si or SiGe, and n-type dopants, such asphosphorus or p-type dopants, such as boron. S/D contact structures 230are disposed on S/D region 210 and within ILD layers 218A-218B and ESL217A. In some embodiments, S/D contact structure 230 can include asilicide layer and a contact plug disposed on the silicide layer. Insome embodiments, via structures (not shown) can be disposed on S/Dcontact structures 230 and within ILD layer 218C and ESL 217B.

Referring to FIGS. 2A-2C, each of gate structures 212 can include aninterfacial oxide (IO) layer 220, a high-k (HK) gate dielectric layer222, a gate metal fill layer 224, and a gate capping layer 226. Gatecontact structure 232 can be disposed on gate structure 212 through ILDlayers 218B-218A, ESL 217B, and gate capping layer 226. In someembodiments, gate contact structure 232 can have dimensions W3-W4 alonga Y-axis greater than dimension W1-W2 along an X-axis. In someembodiments, the ratio of W1:W3 can range from about 1:2 to about 1:4and the ratio of W2:W4 can range from about 1:2 to about 1:4. DimensionsW1 and W3 are dimensions of the top surface of gate contact structure232 and dimensions W2 and W4 are dimensions of the base of gate contactstructure 232. In some embodiments, dimension W1 can range from about 27nm to about 33 nm, dimension W2, which is smaller than dimension W2, canrange from about 20 nm to about 24 nm, dimension W3 can range from about50 nm to about 55 nm, and dimension W4, which is equal to or smallerthan dimension W4, can range from about 50 nm to about 55 nm.

In some embodiments, such dimensions of gate contact structure 232 canbe formed using IBE system 100. The use of IBE system 100 to form gatecontact structure 232 with different dimensions along X- and Y-axis cansimplify the fabrication of gate contact structure 232 and improve itsfabrication process control, as described below. In some embodiments,sidewalls of gate contact structure 232 formed using IBE system 100 canhave different angles with the top surface and base of gate contactstructure 232 along different planes. For example, the sidewalls of gatecontact structure 232 extending along a ZY-plane can form angle A withthe top surface and angle B with the base of gate contact structure 232,as shown in FIG. 2B. On the other hand, the sidewalls of gate contactstructure 232 extending along a ZX-plane can form angle C with the topsurface and angle D with the base of gate contact structure 232, asshown in FIG. 2C. Angle A can be smaller than angle C and angle B can begreater than angle D. As a result, the sidewalls of gate contactstructure 232 along a ZX-plane can be more vertical than the sidewallsof gate contact structure 232 along a ZY-plane. That is, the sidewallsof gate contact structure 232 along a ZX-plane can have a greater slopethan the sidewalls of gate contact structure 232 along a ZY-plane.

FIGS. 2D-2G illustrate cross-sectional views of FET 200 at variousstages of fabricating gate contact structure 232 using IBE system 100,according to some embodiments. The formation of gate contact structure232 can include sequential operations of forming gate contact openings232* (shown in FIGS. 2D-2E) and 232** (shown in FIGS. 2F-2G), fillinggate contact opening 232** with conductive material, and performing achemical mechanical polish (CMP) to form the structures of FIGS. 2A-2C.

Referring FIGS. 2D-2E, gate contact opening 232* is formed in FET 200after the formation of S/D contact structures 230. Gate contact opening232* can be formed on gate metal fill layer 224 by forming a patternedmasking layer 234 (e.g., a photoresist layer) on ILD layer 218C using aphotolithographic process, which can be followed by etching ILD layers2188-218C, ESL 217B, and gate capping layer 226 through patternedmasking layer 234 to form the structures of FIGS. 2D-2E. Gate contactopening 232* can have similar dimensions W1 and W2 along X- and Y-axesand the sidewalls of gate contact opening 232* can have similar angles Balong ZY- and ZX-planes.

The formation of gate contact opening 232* can be followed by theformation of gate contact opening 232**, as shown in FIGS. 2F-2G, usingIBE system 100. Gate contact opening 232** can be formed by performing adirectional etch process of IBE system 100 on the structures of FIGS.2D-2E. The directional etch process of IBE system 100 can expand thedimensions of gate contact opening 232* in one direction along a Y-axis(as shown in FIG. 2G) without changing the dimensions of gate contactopening 232* along an X-axis (as shown in FIG. 2F). As a result,dimensions W1 and W2 of gate contact opening 232* along a Y-axis isexpanded to respective dimensions W3 and W4 of gate contact opening232**. In some embodiments, for the directional etch process, thepressure of IBE system 100 can be set in a range from about 0.15 mT toabout 0.2 mT, a screen grid voltage of 1.2 KV.

In some embodiments, similar to gate contact structures 232, S/D contactstructures 230 can also be formed with different dimensions along X- andY-axes using IBE system 100.

FIGS. 2H-2I illustrate top views of directional etching to form mergedgate contact structure 248 of parallel FETs 241A-241C of semiconductordevice 250 using IBE system 100. Each of FETs 241A-241C can be similarto FET 200. Merged gate contact structure 248 (shown in FIG. 2J) can beformed by connecting gate contact structures 233A-233C of respectiveFETs 241A-241C. Each of gate contact structures 233A-233C can havedimension W1 along an X-axis and dimension W3 along a Y-axis, similar togate contact structure 232.

FIG. 2H illustrates a top view of semiconductor device 250 with parallelFETs 241A-241C after the formation of gate contact openings 231A-231C,similar to gate contact opening 232*. For simplicity, S/D contactstructures 242 and gate contact openings 231A-231C are shown on activelayers 242 of FETs 241A-241C. FETs 241A-241C can be separated from eachother by IDL layer 246. FIG. 2I illustrates a top view of semiconductordevice 250 after the formation of gate contact openings 231A*-231C*using IBE system 100, similar to gate contact opening 232**. Gatecontact openings 231A*-231C* can have dimensions similar to gate contactopening 232**. The formation of gate contact openings 231A*-231C* can befollowed by filling the gate contact openings 231A*-231C* withconductive material to form the merged gate contact structure 248 ofFIG. 2J.

FIG. 3 is a flow chart of a method 300 for performing directionaletching using an IBE system with four or five grids, in accordance withsome embodiments. This disclosure is not limited to this operationaldescription. Rather, other operations are within the spirit and scope ofthe present disclosure. It is to be appreciated that additionaloperations can be performed. Moreover, not all operations may be neededto perform the disclosure provided herein. Further, some of theoperations can be performed simultaneously, or in a different order thanshown in FIG. 3. In some implementations, one or more other operationscan be performed in addition to or in place of the presently describedoperations. For illustrative purposes, method 300 is described withreference to the embodiments of FIG. 1A-1J, or 2A-2J. However, method300 is not limited to these embodiments.

In some embodiments, to perform directional etching, wafer 154 is placedon a rotating fixture 107 in process chamber 101, which can be a vacuumchamber. A gas is introduced through inlet 102. The pressure of processchamber 101 can be reduced in a range from about 0.15 mT to about 0.2mT. An RF plasma generator can be turned on and a plasma is struck(ignited) within plasma chamber 103. Ions are extracted by screen grid110, and further accelerated by accelerator grid 120 as they move towardthe wafer to form ion beams, such as ion beam 141, ion beam 142, and ionbeam 143. The direction of ion beam 141, ion beam 142, ion beam 143 canbe controlled by the a voltage difference between the first deflectorvoltage supplied to deflector plate 135 and the second deflector voltagesupplied to deflector plate 136, or a voltage difference between thefirst deflector voltage supplied to deflector plate 138 and the seconddeflector voltage supplied to deflector plate 139. Ions in the ion beamshit wafer 154, sputtering materials from the surface. The processcontinues until pattern is etched exposing the underlying layer forwafer 154. The high level description of the process is described belowin more details in various operations.

In operation 305 of FIG. 3, a wafer is placed onto a rotating fixturewithin a process chamber of an etching system, where the wafer has atilted angle θ and a rotated angle of α. For example, as shown anddiscussed with reference to FIG. 1A, wafer 154 is placed onto rotatingfixture 107 within process chamber 101 of IBE system 100, where wafer154 has a tilted angle θ and a rotated angle of α.

In operation 310 of FIG. 3, directional etching process parameters ofthe etching system are adjusted. For example, as shown and discussedwith reference to FIG. 1A, directional etching process parameters of IBEsystem 100 are adjusted to have an operation pressure between about 0.15mT to about 0.20 mT for the process chamber, and the tilted angle θbetween about 5° and 60° degrees. In addition, in some embodiments, anetching chemical can be supplied to plasma chamber 103.

In operation 315 of FIG. 3, a screen grid voltage is supplied to ascreen grid element of a screen grid to extract ions from plasma withina plasma chamber of the process chamber to form an ion beam. Forexample, as shown and discussed with reference to FIG. 1B, screen gridvoltage 124 is supplied to screen grid element 111 of screen grid 110 toextract ions from plasma within plasma chamber 103 within processchamber 101 to form ion beam 141.

In operation 320 of FIG. 3, an extraction grid voltage is supplied to anextraction grid element of an extraction grid. For example, as shown anddiscussed with reference to FIG. 1B, extraction grid voltage 125 issupplied to extraction grid element 116 of extraction grid 115. Avoltage difference between screen grid voltage 124 and extraction gridvoltage 125 determines an ion current density of ion beam 141.

In operation 325 of FIG. 3, an accelerator grid voltage is supplied toan accelerator grid element of an accelerator grid. For example, asshown and discussed with reference to FIG. 1B, accelerator grid voltage126 is supplied to accelerator grid element 121 of accelerator grid 120.A voltage difference between extraction grid voltage 125 and acceleratorgrid voltage 126 can determine an ion beam energy for ion beam 141.

In operation 330 of FIG. 3, a decelerator grid voltage is supplied to adecelerator grid element of a decelerator grid. For example, as shownand discussed with reference to FIG. 1B, decelerator grid voltage 127 issupplied to decelerator grid element 131 of decelerator grid 130. Insome embodiments, decelerator grid voltage 127 can be the groundvoltage.

In operation 335 of FIG. 3, directional etching of the wafer isperformed by the ion beam through the hole reaching the wafer. Forexample, as shown and discussed with reference to FIG. 1B, directionaletching of wafer 154 is performed by ion beam 141 through hole 151reaching wafer 154. Operations performed during operation 335 can beviewed as a first phase of directional etching.

In operation 340 of FIG. 3, the wafer is rotated 180° to have a rotatedangle of 180°+α degree while maintaining the tilted angle θ, and asecond phase directional etching is performed on the wafer by the ionbeams. For example, as shown and discussed with reference to FIG. 1A,wafer 154 is rotated 180° to have a rotated angle of 180°+α degree whilemaintaining the tilted angle θ. Moreover, a second phase directionaletching is performed on wafer 154 by the ion beams, such as ion beam141, ion beam 142, and ion beam 143.

In operation 345 of FIG. 3, the wafer is rotated 180° to have therotated angle of a degree while maintaining the tilted angle θ, and thefirst phase of directional etching on the wafer is repeated. Forexample, as shown and discussed with reference to FIG. 1B, wafer 154 isrotated 180° to have the rotated angle of a degree while maintaining thetilted angle θ, and the first phase of directional etching on wafer 154is repeated.

The present disclosure provides example IBE systems (e.g., IBE system100) having a grid system with four grids or five grids (e.g., gridsystem 150) for directional etching to prevent and/or mitigate theasymmetry etching behavior. An IBE system with the example grid systemcan generate improved or close to uniformly distributed etching acrossdifferent locations of a surface of a wafer within the process chamberof the IBE system. The IBE system includes a plasma chamber configuredto provide plasma, a screen grid, an extraction grid, an acceleratorgrid, and a decelerator grid. The screen grid includes a screen gridelement in contact with the plasma chamber. The extraction grid includesan extraction grid element disposed adjacent to and separated from thescreen grid element. The accelerator grid includes an accelerator gridelement disposed adjacent to and separated from the extraction gridelement. The decelerator grid includes a decelerator grid elementdisposed adjacent to and separated from the accelerator grid element.The screen grid element, the extraction grid element, the acceleratorgrid element, and the decelerator grid element form a hole that extendsthrough the screen grid, the extraction grid, the accelerator grid, andthe decelerator grid. The screen grid receives a screen grid voltage toextract ions from the plasma within the plasma chamber to form an ionbeam through the hole. The extraction grid receives an extraction gridvoltage, where an ion current density of the ion beam through the holedepends on a voltage difference between the screen grid voltage and theextraction grid voltage. The accelerator grid receives an acceleratorgrid voltage. An ion beam energy for the ion beam through the holedepends on a voltage difference between the extraction grid voltage andthe accelerator grid voltage. The decelerator grid receives adecelerator grid voltage.

In some embodiments, an IBE system includes a process chamber. Theprocess chamber includes a plasma chamber configured to provide plasma.In addition, the process chamber includes a screen grid, an extractiongrid, an accelerator grid, a decelerator grid, a hole that extendsthrough the screen grid, the extraction grid, the accelerator grid, andthe decelerator grid, and a deflector system includes at least a firstdeflector plate and a second deflector plate separated by a gap. Thescreen grid includes a screen grid element in contact with the plasmachamber. The extraction grid includes an extraction grid elementdisposed adjacent to and separated from the screen grid element. Theaccelerator grid includes an accelerator grid element disposed adjacentto and separated from the extraction grid element. The decelerator gridincludes a decelerator grid element disposed adjacent to and separatedfrom the accelerator grid element. The screen grid element, theextraction grid element, the accelerator grid element, and thedecelerator grid element form a hole that extends through the screengrid, the extraction grid, the accelerator grid, and the deceleratorgrid. The first deflector plate and the second deflector plate aredisposed around the hole. The first deflector plate is configured toreceive a first deflector voltage, and the second deflector plate isconfigured to receive a second deflector voltage. A trajectory of an ionbeam through the hole formed by ions extracted from the plasma withinthe plasma chamber depends on a voltage difference between the firstdeflector voltage and the second deflector voltage.

In some embodiments, a method for directional etching by an IBE systemincludes placing a wafer onto a rotating fixture within a processchamber of the IBE system, where the wafer has a tilted angle θ and arotated angle of α. In addition, the method includes supplying a screengrid voltage to a screen grid element of a screen grid to extract ionsfrom plasma within a plasma chamber of the process chamber to form anion beam. The method further includes supplying an extraction gridvoltage to an extraction grid element of an extraction grid, where anion current density of the ion beam depends on a voltage differencebetween the screen grid voltage and the extraction grid voltage.Moreover, the method includes supplying an accelerator grid voltage toan accelerator grid element of an accelerator grid, where an ion beamenergy for the ion beam depends on a voltage difference between theextraction grid voltage and the accelerator grid voltage. Furthermore,the method includes supplying a decelerator grid voltage to adecelerator grid element of a decelerator grid. The screen grid element,the extraction grid element, the accelerator grid element, and thedecelerator grid element form a hole that extends through the screengrid, the extraction grid, the accelerator grid, and the deceleratorgrid. Afterward, the method includes performing directional etching ofthe wafer by the ion beam through the hole reaching the wafer.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art can better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theycan readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they can make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. An ion beam etching (IBE) system, comprising: aplasma chamber configured to provide plasma; a screen grid comprising ascreen grid element in contact with the plasma chamber; an extractiongrid comprising an extraction grid element disposed adjacent to andseparated from the screen grid element; an accelerator grid comprisingan accelerator grid element disposed adjacent to and separated from theextraction grid element; a decelerator grid comprising a deceleratorgrid element disposed adjacent to and separated from the acceleratorgrid element; and a hole that extends through the screen grid, theextraction grid, the accelerator grid, and the decelerator grid; whereinthe screen grid is configured to receive a screen grid voltage toextract ions from the plasma within the plasma chamber to form an ionbeam through the hole; wherein the extraction grid is configured toreceive an extraction grid voltage and wherein an ion current density ofthe ion beam through the hole depends on a voltage difference betweenthe screen grid voltage and the extraction grid voltage; wherein theaccelerator grid is configured to receive an accelerator grid voltageand wherein an ion beam energy for the ion beam through the hole dependson a voltage difference between the extraction grid voltage and theaccelerator grid voltage; and wherein the decelerator grid is configuredto receive a decelerator grid voltage.
 2. The IBE system of claim 1,further comprising: a deflector system comprising at least a firstdeflector plate and a second deflector plate separated by a gap, whereinthe first deflector plate and the second deflector plate are disposedaround the hole.
 3. The IBE system of claim 2, wherein the firstdeflector plate is configured to receive a first deflector voltage, andthe second deflector plate is configured to receive a second deflectorvoltage, and wherein a trajectory of the ion beam depends on a voltagedifference between the first deflector voltage and the second deflectorvoltage.
 4. The IBE system of claim 3, wherein the trajectory comprisesa tilt angle of the ion beam that depends on the voltage differencebetween the first deflector voltage and the second deflector voltage. 5.The IBE system of claim 2, wherein the deflector system is disposedbetween the extraction grid and the accelerator grid.
 6. The IBE systemof claim 2, wherein the deflector system is disposed adjacent to andseparated from the decelerator grid, and is separated from theaccelerator grid by the decelerator grid.
 7. The IBE system of claim 2,wherein the first deflector plate and the second deflector plate areconfigured to be adjustable in an up direction, a down direction, a leftdirection, or a right direction.
 8. The IBE system of claim 2, whereinthe first deflector voltage has a first voltage polarity, and the seconddeflector voltage has a second voltage polarity that is different fromthe first voltage polarity.
 9. The IBE system of claim 1, wherein thescreen grid voltage and the extraction grid voltage are positivevoltages with respect to a ground voltage; wherein the accelerator gridvoltage is a negative voltage with respect to the ground voltage; andwherein the decelerator grid voltage is the ground voltage.
 10. The IBEsystem of claim 1, further comprising: a control unit configured tosupply the screen grid voltage to the screen grid, supply the extractiongrid voltage to the extraction grid, and supply the accelerator gridvoltage to the accelerator grid.
 11. The IBE system of claim 1, furthercomprising: an other screen grid element of the screen grid, an otherextraction grid element of the extraction grid, an other acceleratorgrid element of the accelerator grid, and an other decelerator gridelement of the decelerator grid; an other hole extending through theother screen grid element, the other extraction grid element, the otheraccelerator grid element, and the other decelerator grid element,wherein an other ion beam from an ion source within the plasma chambergoes through the other hole; and a rotating fixture configured to hold awafer with a tilt angle, wherein the ion beam has a first incidencedistance from the ion source to the wafer, the other ion beam has asecond incidence distance from the ion source to the wafer, and thesecond incidence distance is different from the first incidencedistance.
 12. The IBE system of claim 11, further comprising: amechanical shutter disposed between the plasma chamber and the rotatingfixture, wherein the screen grid, the extraction grid, the acceleratorgrid, and the decelerator grid are disposed between the plasma chamberand the mechanical shutter; a plasma bridge neutralizer configured toprovide electrons to neutralize the ion beam and the other ion beam; anda secondary ions mass spectrometer configured to collect secondary ionsejected from the wafer.
 13. An ion beam etching (IBE) system,comprising: a plasma chamber configured to provide plasma; a screen gridcomprising a screen grid element in contact with the plasma chamber; anextraction grid comprising an extraction grid element disposed adjacentto and separated from the screen grid element; an accelerator gridcomprising an accelerator grid element disposed adjacent to andseparated from the extraction grid element; a decelerator gridcomprising a decelerator grid element disposed adjacent to and separatedfrom the accelerator grid element; a hole that extends through thescreen grid, the extraction grid, the accelerator grid, and thedecelerator grid; and a deflector system includes at least a firstdeflector plate and a second deflector plate separated by a gap, whereinthe first deflector plate and the second deflector plate are disposedaround the hole, wherein the first deflector plate is configured toreceive a first deflector voltage, and the second deflector plate isconfigured to receive a second deflector voltage, and wherein atrajectory of an ion beam through the hole formed by ions extracted fromthe plasma within the plasma chamber depends on a voltage differencebetween the first deflector voltage and the second deflector voltage.14. The IBE system of claim 13, wherein the screen grid is configured toreceive a screen grid voltage to extract the ions from the plasma withinthe plasma chamber to form the ion beam through the hole; wherein theextraction grid is configured to receive an extraction grid voltage andwherein an ion current density of the ion beam through the hole dependson a voltage difference between the screen grid voltage and theextraction grid voltage; wherein the accelerator grid is configured toreceive an accelerator grid voltage and wherein an ion beam energy forthe ion beam through the hole depends on a voltage difference betweenthe extraction grid voltage and the accelerator grid voltage; andwherein the decelerator grid is configured to receive a decelerator gridvoltage.
 15. The IBE system of claim 13, wherein the deflector system isdisposed between the extraction grid and the accelerator grid; ordisposed adjacent to and separated from the decelerator grid, andseparated from the accelerator grid by the decelerator grid.
 16. The IBEsystem of claim 13, further comprising: an other screen grid element ofthe screen grid, an other extraction grid element of the extractiongrid, an other accelerator grid element of the accelerator grid, and another decelerator grid element of the decelerator grid; an other holeextends through the other screen grid element, the other extraction gridelement, the other accelerator grid element, and the other deceleratorgrid element; a third deflector plate of the deflector system and afourth deflector plate of the deflector system separated by an othergap, wherein the third deflector plate and the fourth deflector plateare disposed around the other hole, wherein an other ion beam from anion source within the plasma chamber goes through the other hole; and arotating fixture configured to hold a wafer with a tilt angle, whereinthe ion beam has a first incidence distance from the ion source to thewafer, the other ion beam has a second incidence distance from the ionsource to the wafer, and the second incidence distance is different fromthe first incidence distance.
 17. A method, comprising: placing a waferonto a rotating fixture within a process chamber of an etching system,wherein the wafer has a tilted angle θ and a rotated angle α; supplyinga screen grid voltage to a screen grid element of a screen grid toextract ions from plasma within a plasma chamber of the process chamberto form an ion beam; supplying an extraction grid voltage to anextraction grid element of an extraction grid, wherein an ion currentdensity of the ion beam depends on a voltage difference between thescreen grid voltage and the extraction grid voltage; supplying anaccelerator grid voltage to an accelerator grid element of anaccelerator grid, wherein an ion beam energy for the ion beam depends ona voltage difference between the extraction grid voltage and theaccelerator grid voltage; supplying a decelerator grid voltage to adecelerator grid element of a decelerator grid, wherein the screen gridelement, the extraction grid element, the accelerator grid element, andthe decelerator grid element form a hole that extends through the screengrid, the extraction grid, the accelerator grid, and the deceleratorgrid, and the ion beam goes through the hole; and performing directionaletching of the wafer by the ion beam through the hole to reach thewafer.
 18. The method of claim 17, wherein the performing thedirectional etching of the wafer is a first phase of directionaletching, and the method further comprises: rotating the wafer 180° tohave a rotated angle of 180°+α degree while maintaining the tilted angleθ; and performing a second phase directional etching of the wafer by theion beam.
 19. The method of claim 17, further comprising: supplying afirst deflector voltage to a first deflector plate, and supplying asecond deflector voltage to a second deflector plate, wherein atrajectory of the ion beam depends on a voltage difference between thefirst deflector voltage and the second deflector voltage, the trajectorycomprises a tilt angle of the ion beam that depends on the voltagedifference between the first deflector voltage and the second deflectorvoltage, and wherein the first deflector plate and the second deflectorplate are separated by a gap around the hole through the screen grid,the extraction grid, the accelerator grid, and the decelerator grid; andwherein the first deflector plate and the second deflector plate aredisposed between the extraction grid and the accelerator grid; ordisposed adjacent to and separated from the decelerator grid, andseparated from the accelerator grid by the decelerator grid.
 20. Themethod of claim 17, wherein the performing the directional etching ofthe wafer comprises forming an opening in a hard mask layer on thewafer; and wherein the opening has a first length in a first dimensionand a second length in a second dimension perpendicular to the firstdimension, and wherein the second length is different from the firstlength.